Two common decibel references used to describe sound are sound pressure level (dB SPL), which refers to atmospheric pressure, and A-weighted decibels (dBA), which refer to what the human ear can ...

SPL = 10 log (r/r ref) 2 = 20 log (r/r ref) where r is the given sound pressure and r ref is the reference sound pressure. See: EQUIVALENT ENERGY LEVEL, INTENSITY LEVEL, ISOBEL, NOISE LEVEL, SOUND ...